Quartz crystal elements are used as oscillators, vibrators, surface acoustic wave devices for high frequency filters, light wave guides, semiconductor substrates, or parts thereof. A conventionally known method for manufacturing useful quartz crystal elements comprises a procedure of polishing a quartz single crystal obtained by hydrothermal synthesis to give a thin quartz crystal film. There are other known methods for manufacturing directly quartz crystal thin films, including the sol-gel process, the plasma chemical vapor deposition (CVD) process, the sputtering process, and the laser abrasion process. These manufacturing methods, however, have such problems as a poor yield of practically acceptable quartz crystal thin films and requirements for a large apparatus and strict control of manufacturing conditions. Thus, these methods are not necessarily advantageous as the industrial manufacturing process for quartz crystal thin films.
Japanese Patent Provisional Publication 2002-80296 describes an atmospheric pressure vapor phase epitaxy (AP-VPE) as a method for manufacturing quartz crystal thin films which is advantageously employable in industries. According to the atmospheric pressure vapor phase epitaxy, silicon alkoxide and oxygen are brought into contact with each other to react under atmospheric pressure, without using a vacuum apparatus, preferably in the presence of a catalyst such as hydrogen chloride to grow epitaxially and deposit a quartz crystal thin film on a substrate. The provisional publication further describes that, on forming a quartz crystal thin film on a substrate by the atmospheric pressure vapor phase epitaxy, a buffer layer is formed on the substrate in advance to improve the crystallinity of the depositing quartz crystal thin film thereon.
On the other hand, a quartz crystal thin film which has been grown with a preferentially oriented AT-cut plane is known to exert a particularly low temperature dependency when used as a vibrator and, accordingly, is acceptable as a superior element. There are known, however, no methods for selectively manufacturing a quartz crystal thin film having these characteristic, particularly manufacturing methods using a vapor phase process.